Sublethal effects of antibiosis resistance on the reproductive biology of two spittlebug (Hemiptera: Cercopidae) species affecting Brachiaria spp

Several greenhouse experiments were used to measure how high levels of antibiosis resistance to nymphs in two interspecific Brachiaria (brachiariagrass) hybrids affect life history parameters of the spittlebugs Aeneolamia varia (F.) and Zulia carbonaria (Lallemand), two of the most important spittlebug (Hemiptera: Cercopidae) species affecting Brachiaria production in Colombia. The A. varia-resistant hybrid CIAT 36062, the Z. carbonaria-resistant hybrid SX01NO/0102, and the susceptible accession CIAT 0654 were used to compare the effect of all possible combinations of food sources for nymphs and adults. Calculation of growth indexes showed a significant impact of antibiosis resistance on the biology of immature stages of both species. Median survival times of adults feeding on resistant genotypes did not differ from those recorded on the susceptible genotype, suggesting that factors responsible for high mortality of nymphs in the resistant hybrids did not affect adult survival. Rearing nymphs of A. varia on CIAT 36062 and of Z. carbonaria on SX01NO/0102 had deleterious sublethal effects on the reproductive biology of resulting adult females. It is concluded that high nymphal mortality and subsequent sublethal effects of nymphal antibiosis on adults should have a major impact on the demography of the two spittlebug species studied.     

Antibiosis and tolerance to five species of spittlebug (Homoptera: Cercopidae) in Brachiaria spp.: implications for breeding for resistance

Several genera and species of spittlebugs (Homoptera: Cercopidae) are economic pests of Brachiaria spp. grasses in tropical America. To support current breeding programs aimed at obtaining multiple spittlebug resistance, we undertook a series of studies on antibiosis and tolerance as possible mechanisms of resistance to five major spittlebug species affecting Brachiaria spp. in Colombia: Aeneolamia varia (F.), Aeneolamia reducta (Lallemand), Zulia carbonaria (Lallemand), Zulia pubescens (F.), and Mahanarva trifissa (Jacobi). Four host genotypes, well known for their reaction to A. varia attack, were used to compare their resistance to other spittlebug species: CIAT 0654 and CIAT 0606 (susceptible) and CIAT 6294 and CIAT 36062 (resistant). CIAT 0654 and CIAT 36062 were used in antibiosis studies. Tolerance studies were conducted with CIAT 0654, CIAT 6294, and CIAT 36062. Sixty-five hybrid-derived clones were used to identify levels of multiple resistance to three spittlebug species. The levels of antibiosis resistance in CIAT 36062 clearly differed by spittlebug species and were classified as follows: very high for M. trifissa, high for A. varia and A. reducta, moderate for Z. pubescens, and absent for Z. carbonaria. Our results suggest the presence of true tolerance to Z. carbonaria in CIAT 6294 and CIAT 36062, true tolerance to Z. pubescens in CIAT 6294 and a combination of tolerance and antibiosis as mechanisms of resistance to Z. pubescens in CIAT 36062. Of the 65 hybrid clones tested with A. varia, A. reducta, and Z. carbonaria, 15 combined resistance to two species and three showed antibiosis resistance to all three spittlebug species.     

Response of resistant and susceptible Brachiaria spp. genotypes to simultaneous infestation with multiple species of spittlebugs (Hemiptera: Cercopidae)

The response of one susceptible and three resistant Brachiaria spp. (Hemiptera: Cercopidae) genotypes to individual or combined attacks by nymphs of Aeneolamia varia (F.), Aeneolamia reducta (Lallemand), Zulia carbonaria (Lallemand), and Zulia pubescens (F.) was studied. We assessed the effect of infesting plants of the susceptible check BRX 44-02 and of the A. varia-resistant genotypes CIAT 6294 and CIAT 36062 with A. varia, Z. carbonaria, or Z. pubescens either alone or in two-species combinations. In a second trial, we studied the performance of BRX 44-02, CIAT 6294, and the multiple resistant clone SX01NO/0102 exposed to individual or combined attack by A. reducta and Z. carbonaria. In a third trial, we compared the response of BRX 44-02, CIAT 6294, and CIAT 36062 to individual A. varia, Z. carbonaria, or Z. pubescens attack as opposed to a combined three-species attack. Plant damage scores and percentage of nymphal survival were recorded in all three trials. Data on percentage of survival indicated that competition between and among spittlebug species occurs. However, we found no evidence of interaction between species competition and different levels of resistance to spittlebug. Rather, host genotype reactions conformed to previously known categories of resistance regardless of the presence of more than one spittlebug species. Resistance rather than competition seems to have been the overriding factor determining nymph survival and resistance expression (damage scores) in these experiments. Our results corroborate the need to develop brachiariagrass genotypes with multiple resistance to spittlebugs.     

Independence of resistance in Brachiaria spp. to nymphs or to adult spittlebugs (Hemiptera: Cercopidae): implications for breeding for resistance

Both nymphal and adult spittlebugs (Hemiptera: Cercopidae) cause serious economic damage to susceptible brachiariagrass [genus Brachiaria (Trin.) Griseb], pastures in tropical America. Both life stages are xylem feeders: nymphs feed primarily on roots and stems, whereas the adults feed mainly on foliage. Numerous interspecific brachiariagrass hybrids with high levels of antibiosis resistance to nymphs of several important spittlebug species have been obtained. Recent studies revealed major inconsistencies between reaction to nymphs and reaction to adults on the same host genotype. Because both insect life stages can cause severe economic damage on susceptible brachiariagrass pastures, a cultivar development strategy must take into account resistance to both life stages. To assess the degree of association between resistance to spittlebug nymphs and to adult feeding, we tested 164 hybrids and six check genotypes for resistance to both life stages of three spittlebug species: Aeneolamia varia (F.), Aeneolamia reducta (Lallemand), and Zulia carbonaria (Lallemand). Most hybrids tested were classified as resistant to nymphs. On the contrary, for all three species, the overall mean damage score of the 164 hybrids did not differ from the mean score of the susceptible checks. None of the hybrids was classified as resistant to adult feeding damage. Correlations between percentage nymph survival and adult damage scores were consistently low (r = 0.0104-0.0191). Correlations between nymphal and adult damage scores were also low (0.109-0.271), suggesting that resistances to the different life stages are largely independent. Chi-square analyses comparing frequency distributions of responses of the 164 breeding hybrids to nymphs or adults confirmed essential genetic independence of these two traits. We conclude that attention to improving genetic resistance specifically to adult feeding damage is warranted.     

Secretion of phytase from the roots of several plant species under phosphorus-deficient conditions

Phosphorus (P) deficiency increased the secretion of phytases from roots of various plant species. The secretory phytases were collected with a dialysis membrane tube for 24 hours from roots of sixteen plant species grown with low or adequate supply of P in nutrient solutions. The activity of not only secretory phytase, but also acid phosphatase, increased with the low P treatment in all of the plant species examined. Secretion of phytase by the roots under P-deficient conditions was highest in Brachiaria decumbens CIAT 606, Stylosanthes guianensis CIAT 184 and tomato, moderate in Brachiaria brizantha CIAT6780, Stylosanthes guianensis CIAT 2950, alfalfa, white clover and orchard grass, and lowest in Andropgon gayanus CIAT 621, Stylosanthes capitata CIAT 10280, upland rice, timothy, redtop, alsike clover, red clover and white lupin plants. An immunoreactive protein band that reacted with a polyclonal antibody raised against wheat bran phytase, corresponding to molecular weight 35–40 kD, could be detected in seven of the species tested. These results indicate that the secretory phytase may provide an efficient mechanism for certain plants to utilize inositol hexaphosphate in soil.     

Resistance of cabbage (Brassica oleracea capitata group) crops to Mamestra brassicae

Twenty-one cabbage (Brassica oleracea capitata group) varieties, including 16 local varieties and five commercial hybrids, were screened for resistance to the moth Mamestra brassicae L. under natural and artificial conditions in northwestern Spain. Resistance was assessed as the proportion of damaged plants and damaged leaves, leaf feeding injury, and number of larvae present. Correlation coefficients among damage traits showed that a visual scale (general appearance rating) should be a useful indicator of resistance. Most local varieties were highly susceptible to M. brassicae, whereas the commercial hybrids tested were resistant in terms of head foliage consumption and number of larvae per plant. Performance of varieties was similar under natural and artificial infestation although some of them performed differently at each year. Three local varieties (MBG-BRS0057, MBG-BRS0074, and MBG-BRS0452) were highly susceptible at both natural and artificial infestation conditions being MBG-BRS0074 the most damaged variety. Two local varieties (MBG-BRS0402 and MBG-BRS0535) and commercial hybrids were identified as resistant or moderately resistant to M. brassicae. Among them, 'Corazón de Buey' and 'Cabeza negra' were the most resistant and produced compact heads. These varieties could be useful sources of resistance to obtain resistant varieties to M. brassicae or as donors of resistance to other Brassica crops. The possible role of leaf traits, head compactness, and leaf glucosinolate content in relation to M. brassicae resistance is discussed.     

Impact of plant resistance on southwestern corn borer (Lepidoptera: Crambidae) biology and plant damage

Southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), is a major insect pest of corn, Zea mays L., in the southern United States. Germplasm lines with resistance to southwestern corn borer have been developed and released by the USDA-ARS. Two single-cross hybrids produced by crossing germplasm lines with resistance to southwestern corn borer and a susceptible single-cross hybrid were infested with southwestern corn borer larvae in a 2-yr field test conducted in Mississippi. The susceptible hybrid sustained significantly more leaf damage and stalk tunneling than either resistant hybrid. The number of tunnels and the length of tunneling were significantly lower on the resistant hybrids. In 2003, up to 15 times more tunneling was observed on the susceptible hybrid. Larvae feeding on the resistant hybrids were delayed in their movement from the whorl to the stalk and larval survival was 50% lower on the resistant hybrids than on the susceptible hybrid. Larvae recovered from the susceptible hybrid 7-14 d after infestation weighed twice as much as those recovered from the resistant hybrids. Similar differences in larval weight were observed in the laboratory when larvae were reared on diets prepared from lyophilized tissue from the three hybrids. These results provide a foundation for other investigations designed to identify and determine the roles of specific genes and gene families associated with southwestern corn borer resistance in corn.     

Phenological and chemical differences among hybrid poplar clones (Salicaceae) varying in resistance to Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae)

Hybrid poplars with Populus maximowiczii parentage have demonstrated antixenotic resistance against adult poplar-and-willow borers, Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae), in the summer, and antibiosis against C. lapathi larvae in the spring. We examined phenological and biochemical differences among hybrid poplars with and without P. maximowiczii parentage that are resistant and susceptible, respectively, to C. lapathi, to test the hypotheses that resistance was due to physical hydraulic forces, inadequate nutrition, or abundant secondary metabolites. The hybrids with P. maximowiczii parentage flushed earlier than susceptible hybrids, but no differences were found between hybrids with respect to sap flow or bark moisture content that could explain larval mortality in the spring. Similarly, constitutive levels of nutritive compounds (sitosterol, nitrogen, linoleic and linolenic acids, and carbohydrates) were lower or not different in the most susceptible hybrid TN 302-9. Thus, all hybrids appear to be nutritionally sound. TN 302-9 contained the highest constitutive levels of condensed tannins and catechin, but overall phenolic glycoside levels (salicin and salicortin) were similar among all hybrids, with the exception of one sampling date; however, this difference would not likely explain resistance. Neither induced or constitutive polyphenol oxidase (PPO) activity nor induced levels of secondary metabolites could explain resistance. Thus, we conclude hybrids that contain P. maximowiczii parentage have a novel mechanism for resistance.     

Effect of sorghum resistant to Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) on oviposition and development of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract Helicoverpa armigera oviposition preference for, and larval development on sorghum hybrids with differing resistance to sorghum midge, Stenodiplosis sorghicola , were investigated. When H. armigera larvae were fed seed of resistant and susceptible hybrids in the laboratory there were no differences in larval and pupal sizes or the rate of development. The same result was recorded when larvae fed on panicles on plants in a glasshouse. On some sampling occasions, significantly more eggs were laid on panicles of resistant hybrids in the field. This occurred when plants were in plots and also in a mixed planting. Midge-resistance status did not affect levels of egg parasitism. In a field study using recombinant inbred lines between a midge-resistant and a midge-susceptible line, no relationship was found between level of resistance and oviposition of H. armigera . We conclude that, although midge-resistant hybrids are sometimes preferred for oviposition by H. armigera, the resistance per se does not determine this preference. Egg survival, larval survival, development and resultant damage are not significantly affected by the midge-resistance status of the host.     

Loss of notum macrochaetae as an interspecific hybrid anomaly between Drosophila melanogaster and D. simulans.

With the aim of revealing genetic variation accumulated among closely related species during the course of evolution, this study focuses on loss of macrochaetae on the notum as one of the developmental anomalies seen in interspecific hybrids between Drosophila melanogaster and its closely related species. Interspecific hybrids between a line of D. melanogaster and D. simulans isofemale lines exhibited a wide range in the number of missing bristles. By contrast, D. mauritiana and D. sechellia lines showed almost no reduction in bristle number in hybrids with D. melanogaster. Genetic analysis showed that the D. simulans X chromosome confers a large effect on hybrid bristle loss, although X-autosome interaction may be involved. This suggests that at least one genetic factor contributing to hybrid anomalies arose recently on a D. simulans X chromosome. Moreover, the results indicate sex dependency: the male hybrids were more susceptible to bristle loss than the female hybrids were. Use of cell type markers suggests that the defect does not lie in cell fate decisions during bristle development, but in the maintenance of neural fate and/or differentiation of the descendants of sensory mother cells.     

Biochemical characterization of hydrolytic and oxidative enzymes in insecticide resistant and susceptible strains of the German cockroach (Dictyoptera: Blattellidae).

We have identified resistance mechanisms in the German cockroach, Blattella germanica (L.), for propoxur and chlorpyrifos in strains of cockroaches that display multiresistance to several organophosphate and carbamate insecticides. The resistance mechanisms involve the combined effects of increased oxidative and hydrolytic metabolism and both strains are resistant to chlorpyrifos and propoxur. Experiments designed to test for similarity in metabolic enzymes suggest that, although the mechanisms involve similar processes, the enzymes responsible for insecticide detoxification are different in the two strains. Both resistant strains exhibited enhanced activity toward alpha-naphtholic esters relative to a standard susceptible strain; however, analysis of the progeny from resistant X susceptible crosses suggests that this general esterase activity is inherited differently than propoxur or chlorpyrifos resistance. Hybrids of the propoxur-resistant strain displayed the highest activity of all cockroaches tested, in contrast to hybrids of the chlorpyrifos-resistant strain, which were similar to the susceptible strain. Native gel electrophoresis of cytosolic preparations provided further evidence for differences in the pattern of hydrolytic enzymes and inheritance of resistance in the two strains. Analysis of components of the cytochrome P450-dependent monooxygenase system and activities toward model substrates indicate that the two resistance mechanisms also involve different oxidative processes. The propoxur-resistant strain displayed significantly higher levels of total cytochrome P450, but no other components were correlated with resistance. In contrast with the chlopyrifos-resistant strain, which was similar to the susceptible strain in all parameters measured, activity toward model substrates was higher in the propoxur-resistant strain than in any of the other strains and hybrids tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of epicuticular waxes of poplar hybrids on the aphid Chaitophorus leucomelas (Hemiptera: Aphididae)

Abstract:  Insect response to plant surface features is a critical step in host-finding and acceptance of herbivorous insects. The plant surface is usually covered with epicuticular waxes (EWs), which are not only involved in water physiology, but also provide resistance to insects. In the present work the probing behaviour and performance of the aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) on dewaxed and waxed leaves of two poplar hybrids, [( Populus trichocarpa Torr. & Gray ×  Populus deltoides Bartram ex Marshall) ×  P. deltoides ] (TD × D) and [( P. trichocarpa  ×  Populus maximowiczii Henry) × ( P. trichocarpa  ×  P. maximowiczii )] (TM × TM), previously reported as susceptible and resistant, respectively, are described. Laboratory experiments showed that in naturally waxed leaves of the resistant hybrids, aphids devoted less time to probing and more time to non-probing behaviour when compared with their behaviour on susceptible hybrids. These differences were not present when leaves of these hybrids were experimentally dewaxed. A field experiment demonstrated that aphid reproductive performance was affected by hybrid genotype (higher in the TD × D) but not by EWs, although a trend of lower performance on dewaxed leaves in both hybrids was apparent. SEM analysis of EWs revealed micromorphological differences between both hybrids. These results support the idea that EWs affect aphid behaviour in poplars, with a rather slight impact on reproductive performance.     

Studies of sibling Drosophila species from Laguna Verde, Veracruz, Mexico: I. Species frequencies, viability, desiccation resistance, and vagility

The sibling species Drosophila melanogaster and D. simulans were collected at Laguna Verde, Veracruz, Mexico. D. melanogaster was found in significantly greater frequency than was D. simulans. Ten isofemale lines of each species were tested for egg to adult viability, desiccation resistance, and vagility. D. melanogaster surpassed D. simulans in all three characteristics. The findings are discussed with reference to the climatic conditions at Laguna Verde and the expected effect of such an environment on the relative frequencies of these species. The dichotomous results in regard to desiccation resistance and vagility that were observed between recently collected D. melanogaster and the Oregon-R laboratory stock of that species are also discussed.     

Genetic transfer of a twospotted spider mite (Acari: Tetranychidae) repellent in tomato hybrids

Lycopersicon hirsutum Dunal is very resistant to arthropod herbivory, and research on causes of resistance has often implicated trichomes and their secretions. To better understand relationships among resistance, repellency, and 2,3-dihydrofarnesoic acid, a trichome-borne sesquiterpenoid spider mite repellent, two tomato, Lycopersicon esculentum Miller, varieties were interbred with a highly resistant, spider mite repellent accession (LA1363) of L. hirsutum. Backcross and F2 generations were produced with each tomato variety. Whole leaves of 99 hybrids were bioassayed with twospotted spider mites, Tetranychus urticae Koch, allowing selection of six hybrids (two susceptible and four resistant) for each generation of each family. When these 24 hybrids were characterized for spider mite repellency with thumbtack bioassays, two hybrids had repellent leaflets, demonstrating that repellency was genetically transferred to interspecific tomato hybrids. Leaflet washes containing trichome secretions from each of three hybrids, including the two having repellent leaflets, were repellent in bridge bioassays. For the two hybrids having repellent leaflets and leaflet washes, removal of trichome secretions by dipping leaflets in methanol eliminated leaflet repellency. 2,3-Dihydrofarnesoic acid was present in trichome secretions of the hybrids having leaflet repellency, and it also was present in secretions of other hybrids, indicating that its presence is essential, but not sufficient for leaflet repellency. With regard to resistance, 16 of the hybrids tested had been identified as resistant in a whole leaf bioassay, but only two had repellent leaflets, indicating that other mechanisms of resistance are present in the resistant L. hirsutum parent.     

Comparison of Triazine-Resistant and -Susceptible Biotypes of Senecio vulgaris and Their F(1) Hybrids

The relationship of triazine resistance to decreased plant productivity was investigated in Senecio vulgaris L. F₁ reciprocal hybrids were developed from pure-breeding susceptible (S) and resistant (R) lines. The four biotypes (S, S × R, R, R × S) were compared in terms of atrazine response, electron transport, carbon fixation, and biomass production. Atrazine response, carbon fixation rate, and PSII and whole-chain electron transport rates of hybrids were nearly identical to those of their respective maternal parents. Significant differences occurred between the two susceptible (S, S × R) and two resistant (R, R × S) biotypes in atrazine response (I₅₀), carbon fixation rate, and PSII and whole-chain electron transport rates; PSI rates were identical in all four biotypes. Coupled and uncoupled, whole-chain electron transport rates of thylakoids of the two susceptible biotypes were approximately 50% greater than those of the two resistant biotypes at photon flux densities greater than 215 micromoles per square meter per second. Carbon exchange rates of the two susceptible biotypes were 23% greater than those of the two resistant biotypes. Hybrid biotypes (S × R, R × S) were not identical to their maternal parents in biomass production. The S, S × R, and R × S plants all achieved greater biomass than R plants. These results suggest that while the resistance mutation influences thylakoid performance, reduced productivity of triazine-resistant plants cannot be ascribed solely to decreases in electron transport or carbon assimilation rates brought about by the altered binding protein. Since the F₁ hybrids differed from their maternal parents only in nuclear genes, it appears that the detrimental effects of the triazine resistance mutation on plant growth may be attenuated by interactions of the plastid and nuclear genomes.     

Seasonal abundance of Tuberolachnus salignus and its effect on flowering of host willows of varying susceptibility

The giant willow aphid Tuberolachnus salignus Gmelin is a large phloem-feeding insect which colonizes the stems of willow trees. This aphid is a new invasive species in New Zealand and there is limited knowledge of its inter-annual population patterns and the damage it can cause to willow hosts. Our study investigated the T. salignus population dynamics and its effects on the flowering parameters of fifteen willow species and hybrids in a field trial. The aphid population levels were found to vary among the willow species and hybrids. Based on the aphid population levels, the willow species and hybrids were classified as resistant, moderately resistant, susceptible or highly susceptible. T. salignus infestation had no effect on the flowering of resistant and moderately resistant willows, but significantly delayed the flowering time, extended the flowering duration, and decreased the catkin length in susceptible species and hybrids. Interestingly, aphid infestation was found to increase the catkin number and total floral output of some willow species and hybrids. It can be concluded that aphid populations and their effects on flowering are host-specific, with large differences between resistant and susceptible host plants.     

Phenotypic and histochemical traits of the interaction between Plasmopara viticola and resistant or susceptible grapevine varieties

ABSTRACT: BACKGROUND: Grapevine downy mildew, caused by Plasmopara viticola, is a very serious disease affectingmainly Vitis vinifera cultivated varieties around the world. Breeding for resistance throughthe crossing with less susceptible species is one of the possible means to reduce the diseaseincidence and the application of fungicides. The hybrid Bianca and some of its siblings areconsidered very promising but their resistance level can vary depending on the pathogenstrain. Moreover, virulent strains characterized by high fitness can represent a potential threatto the hybrid cultivation. RESULTS: The host response and the pathogen virulence were quantitatively assessed by artificiallyinoculating cv Chardonnay, cv Bianca and their siblings with P. viticola isolates derived fromsingle germinating oospores collected in various Italian viticultural areas. The hostphenotypes were classified as susceptible, intermediate and resistant, according to the AreaUnder the Disease Progress Curve caused by the inoculated strain. Host responses in cvBianca and its siblings significantly varied depending on the P. viticola isolates, which in turndiffered in their virulence levels. The fitness of the most virulent strain did not significantlyvary on the different hybrids including Bianca in comparison with the susceptible cvChardonnay, suggesting that no costs are associated with virulence. Among the individualfitness components, only sporangia production was significantly reduced in cv Bianca and insome hybrids. Comparative histological analysis revealed differences between susceptibleand resistant plants in the pathogen diffusion and cytology from 48 h after inoculation onwards. Defence mechanisms included callose depositions in the infected stomata, increasein peroxidase activity, synthesis of phenolic compounds and flavonoids and the necrosis ofstomata and cells immediately surrounding the point of invasion and determined alterations inthe size of the infected areas and in the number of sporangia differentiated. CONCLUSIONS: Some hybrids were able to maintain an intermediate-resistant behaviour even wheninoculated with the most virulent strain. Such hybrids should be considered for further fieldtrials.     

Genes tagging and molecular diversity of red rot susceptible/tolerant sugarcane hybrids using c-DNA and unigene derived markers

Sugarcane is an important international commodity as a valuable agricultural crop especially in tropical and subtropical countries. Two bulked DNA used to screen polymorphic primers from commercial hybrids (varieties) with moderately resistant and highly susceptible to red rot disease. Among 145 simple sequence repeat and unigene primers screened, 37 (25%) were found to be highly robust and polymorphic with Polymorphism Information Content values ranging from 0.50 to 1.00 with the mean value of 0.82. Among these microsatellites, twenty one were used in the study of genetic relationships and marker identification in sugarcane varieties for red rot resistance. A total of 105 polymorphic DNA bands were identified, with their fragment size ranging from 54 to 1,280 bp. Jaccard’s similarity coefficient value recorded between closely related hybrids was 0.986 while lowest coefficient value of 0.341 was detected with distantly related hybrids. The average similarity coefficient among these hybrids was 0.663. Cluster analysis resulted in a dendrogram with two major clusters separating the moderately resistant varieties from highly susceptible varieties. Three group specific fragments amplified by unigene Saccharum microsatellite primers viz; two markers UGSM316₈₅₀ and UGSM316₆₀ were closely associated with moderately resistant varieties by appearing bands in this region but the bands were absent in highly susceptible varieties. Similarly UGSM316₄₀₀ marker was tightly linked with highly susceptible varieties by amplifying uniformly in sugarcane varieties showing highly susceptible reaction to red rot but it was absent in moderately resistant varietal groups. Validation of red rot resistance/susceptibility associated markers on a group of different mapping populations for red rot resistant/susceptible traits is in progress.     

Inheritance of resistance against northern leaf blight of maize using conventional breeding methods

Maize (Zea mays L.) is one of the important cereal crops along with wheat and rice worldwide. The purpose of this study was to use classical genetic approaches to assess the resistance of various maize parents and hybrids to the northern corn leaf blight (NCLB) disease in two different locations in Egypt. Eight parents, 28 F1, and 2 check hybrids were evaluated. The analysis of variance showed high significant variations between maize parents and their hybrids for the studied parameters and NCLB disease, besides there are significant variations between both locations. Results of maize parents showed that Sids 63, Giza 602, and Giza 628 cultivars exhibited the highest values and were resistant to NCLB in both locations comparing with Nubaria 39 and Gemmiza 18 that were susceptible to NCLB disease. Concerning the maize hybrids, analysis of variance and mean squares of growth characters in both locations indicated high significant variations between the maize hybrids including the check hybrids. When combined between the two locations for current parameters against NCLB, the data pointed that the Sakha location values for maize hybrids were much closed to the combining data in parents and the hybrids detected high resistance to this disease comparing with Nubaria location. All tested maize lines (38 lines), including parents and hybrids were classified as follows, two lines were rated as 1 (highly resistant), three were rated as 2 (resistant), sixteen were rated as 3 (moderate resistant), eight were rated 4 (moderately susceptible) and nine were rated 5 (susceptible). The data explaining that the crossing between high resistant maize cultivars produced high levels of resistance to NCLB disease. Therefore, our results verified that classical breeding could efficiently increase the resistance levels of maize germplasm against NCLB disease by developing new cultivars with superior performance in terms of grain yield, disease resistance and grain quality.     

吉林省部分玉米种质资源抗玉米弯孢菌叶斑病鉴定研究

玉米弯孢菌叶斑病主要是由弯孢菌（Curvularia lunata）引起的侵染性病害。近年来,该病害在我国玉米主产区发生面积逐年扩大,已成为玉米重要病害之一。本文研究了吉林省主要玉米杂交种和自交系抗病性差异,结果表明：玉米杂交种间以及自交系间抗病性差异明显;吉63、黄早4、自330、丹9046、丹9041、铁7922、掖478、沈5003、丹340和E28等一批应用多年的种质资源均为感病类型（MS-HS）;而新选育的各类群一些种质和具有热带、亚热带血缘的78599等一些外来种质资源均为抗病类型（R～HR）。杂交种的抗病性与双亲的抗病性有密切关系;玉米杂交种苗期较抗病,抽丝期极为感病,这表明杂交种抗性随植株生长而递减。